When I fired it up the CPU was set to ~1.2V and the memory to 1.5V and with just the WinXP screen it was at 46W, pretty good. I set the CPU to 1.0V and the memory to 1.3V, no 1.35V setting. Back to WinXP 46W, why no change? I went back into the BIOS and sure enough my changes were there: CPU 1.008V, memory 1.34V.

While changing voltage settings will help, it doesn't make that much a difference at idle as it used to. For starters, RAM is pretty low on power consumption as-is. Also, with the Nehalem microarchitecture (in this case, Clarkdale), the CPU has very good power gating, meaning that instead of the cores sitting at 1.3v or 1.0v during idle, they probably have nearly no voltage going to them at all. This is all to say that while undervolting will definitely help your load power consumption, idle power consumption is already very low so undervolting will not help too much.

Other than underclocking/undervolting the CPU, memory, VGA, PCI, another thing you could do is turn off all the unnecessary onboard stuff like audio, IDE channels, parallel port etc... But I doubt that will make any measurable difference. There's only so much you can do on the software side before hardware becomes your limiting factor.

I think the idea is green. A lot of computers idle a lot, some close to 24/7 so all that can be done is good to do. Reducing voltage doesn't have much efficiency but even a bit is good when done in several computers. To reduce any computers power consumption (and heat & sound level at the same time, of cource), here's some basics for everybody:

TO DO list:

1. Remove normally unused programs from the startup list (and those you never use totally away from the hard drives).

2. Change your backround to totally back. No need for a screen saver after that either. Use blackle instead of google when you search.

3. Disable or uninstall or all the unnecessary windows behaviours (AERO for example). If you don't need indexes of your drives, disable them too.

4. Setup each piece of hardware to shut themselves down after a while. Most important are screen and HDD. In windows 7: Open control panel -> power management -> change... -> advanced

5a. (without an option to change computer speed on the fly)
Enter your BIOS and underclock your computer to minimum what you need to run all your programs nicely. Try your most demanding game or other program to find the minimum setting.

5b. (with option to change speed on the fly)
If you have uGuru or other tool to change the computer speed on the fly, enter your BIOS first and underclock to minimum you can just to start windows nicely. Leave your voltage settings to AUTO DETECT. After that use your "on the fly" tool to set each of your programs to change the computer speed for what they need to run smoothly.

6a. (without an option to change speed on the fly) Enter your BIOS and disable automatic voltage discovering. Start lowering voltages one step at a time until you find the last stabile undervolting setup. The voltages you want to change are: CPU Core, CPU VTT, DIMM, Northbridge Core, Southbridge core. Do not change voltages which are supposed to be in certain level (1,5V; 3,3V;5V;12V) unless they are over their level.

6b. (with option to change speed on the fly) Don't change your voltages in BIOS, instead make sure that the AUTO detection is on. Otherwise the change in speed made by uGuru or other program might make your computer unstable.

7. Run any tool to check your temperatures at IDLE load and after a 15 min MAX load. After the check use another tool (like speedfan) to set your fan speeds as low as possible. In some cases you can even unplug some of the fans (if MAX load doesn't get the temperatures near their limits).

8. In the end make sure you run a stability test for at least 8h with MAX load to make sure that the temperatures don't get too high. If you're busy, already 2h gives you an idea if the computer is still stabile but you can never be too sure.

IDLE (slow settings)
1 fan running at 150rpm, one at 300rpm and 3 at 600rpm. E8400 (normally 3.0GHz) is set to run at 6x267 (1,6GHz). Memory is undervolted to 533MHz (2x267). All temperatures are between 35-40.
My idle power is at 5A.

MAX LOAD (slow settings)
When I watch HD movies or do something else that doesn't require a lot from the processor or the memory, I use the same minimum settings. The temperatures never get over 60 (8h stress tested). A stress test with these setting gives me 24A power consuption.

MAX LOAD (fast settings)
When I want to play nicely I let my uGuru to run in turbo mode. Clock is set to 9x400 (3,6GHz) and memory is running at DDR2 800 (2x400). Since my memory is OC-style, i have tested to run it as DDR2 1066 but nothing that I do doesn't look/feel any better with these voltages, so i'm happy with DDR2 800. A stress test with these settings give me a power reading of 42A. All temperatures still stay under 60 degrees, but fans spin a bit faster. The system is still quiet. At IDLE power reading seems to be 6A.

CONCLUSIONI'm saving 1/6 energy all the time and almost 1/2 when watching movies (enjoing the extreme quietness at the same time, of cource). I suggest you do something too, it's easy to follow my steps to number 4. (I suppose people who read this forum are ready to go to number .

QUESTION to remainDoes anyone know a program to shut down and start fans depending on the desired temperature readings? I'd like it to work on my MB (abit IX38 quadGT, uGuru) which has a lot of temperature sensors and place for 6 fans and

I think the idea is green. A lot of computers idle a lot, some close to 24/7 so all that can be done is good to do. Reducing voltage doesn't have much efficiency but even a bit is good when done in several computers. To reduce any computers power consumption (and heat & sound level at the same time, of cource), here's some basics for everybody:

TO DO list:

1. Remove normally unused programs from the startup list (and those you never use totally away from the hard drives).

2. Change your backround to totally back. No need for a screen saver after that either. Use blackle instead of google when you search.

3. Disable or uninstall or all the unnecessary windows behaviours (AERO for example). If you don't need indexes of your drives, disable them too.

4. Setup each piece of hardware to shut themselves down after a while. Most important are screen and HDD. In windows 7: Open control panel -> power management -> change... -> advanced

5a. (without an option to change computer speed on the fly)Enter your BIOS and underclock your computer to minimum what you need to run all your programs nicely. Try your most demanding game or other program to find the minimum setting.

5b. (with option to change speed on the fly)If you have uGuru or other tool to change the computer speed on the fly, enter your BIOS first and underclock to minimum you can just to start windows nicely. Leave your voltage settings to AUTO DETECT. After that use your "on the fly" tool to set each of your programs to change the computer speed for what they need to run smoothly.

6a. (without an option to change speed on the fly) Enter your BIOS and disable automatic voltage discovering. Start lowering voltages one step at a time until you find the last stabile undervolting setup. The voltages you want to change are: CPU Core, CPU VTT, DIMM, Northbridge Core, Southbridge core. Do not change voltages which are supposed to be in certain level (1,5V; 3,3V;5V;12V) unless they are over their level.

6b. (with option to change speed on the fly) Don't change your voltages in BIOS, instead make sure that the AUTO detection is on. Otherwise the change in speed made by uGuru or other program might make your computer unstable.

7. Run any tool to check your temperatures at IDLE load and after a 15 min MAX load. After the check use another tool (like speedfan) to set your fan speeds as low as possible. In some cases you can even unplug some of the fans (if MAX load doesn't get the temperatures near their limits).

8. In the end make sure you run a stability test for at least 8h with MAX load to make sure that the temperatures don't get too high. If you're busy, already 2h gives you an idea if the computer is still stabile but you can never be too sure.

IDLE (slow settings)1 fan running at 150rpm, one at 300rpm and 3 at 600rpm. E8400 (normally 3.0GHz) is set to run at 6x267 (1,6GHz). Memory is undervolted to 533MHz (2x267). All temperatures are between 35-40.My idle power is at 5A.

MAX LOAD (slow settings)When I watch HD movies or do something else that doesn't require a lot from the processor or the memory, I use the same minimum settings. The temperatures never get over 60 (8h stress tested). A stress test with these setting gives me 24A power consuption.

MAX LOAD (fast settings)When I want to play nicely I let my uGuru to run in turbo mode. Clock is set to 9x400 (3,6GHz) and memory is running at DDR2 800 (2x400). Since my memory is OC-style, i have tested to run it as DDR2 1066 but nothing that I do doesn't look/feel any better with these voltages, so i'm happy with DDR2 800. A stress test with these settings give me a power reading of 42A. All temperatures still stay under 60 degrees, but fans spin a bit faster. The system is still quiet. At IDLE power reading seems to be 6A.

CONCLUSIONI'm saving 1/6 energy all the time and almost 1/2 when watching movies (enjoing the extreme quietness at the same time, of cource). I suggest you do something too, it's easy to follow my steps to number 4. (I suppose people who read this forum are ready to go to number .

QUESTION to remainDoes anyone know a program to shut down and start fans depending on the desired temperature readings? I'd like it to work on my MB (abit IX38 quadGT, uGuru) which has a lot of temperature sensors and place for 6 fans and

I did not read everything but the reason you see no change is that the motherboard will under-volt the CPU automatically depending on use so at idle the CPU will be 0.8 to 1V depending on the CPU but when the CPU is loaded 100% the voltage will go back to 1.2V or what is the default setting.
If you manually under-volt the CPU you will not see to much gain at idle since the voltage will always be at the set value 1V in your case so no variation and you will only see a difference in power consumption at load.

About LCD monitors black is not always using more energy see Link but most panels are TN and those use less with a white screen but if you have an IPS screen then it will use less with a black screen I do not know about PVA panels.

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